Carbon dioxode is inexpensive, highly abundant and can be used as a C1 feed stock for the synthesis of cyclic carbonates, polycarbonates etc. These transformations are attractive processes from the view of point “green chemistry” because CO2, a global warming gas, can be incorporated without any side product and also it is a renewable C1 source. Organic cyclic carbonates have been widely used as monomers, aprotic organic solvents, pharmaceutical/fine chemical intermediates, electrolytic components, chemical intermediates etc. and are also useful in many biomedical applications. Cyclic carbonates are also used to synthesis dialkyl carbonates which are of industrial importance for many potential applications.
Several catalytic materials including amines, phosphines, metal oxides have been reported in the recent years for the synthesis of cyclic carbonates from CO2. Transition metal ion based catalysts in conjunction with a Lewis base have been reported to be efficient for the CO2 fixation reaction. A substantial number of patents and articles are available in the literature which describe production of alkylene carbonates from alkylene oxides and carbon dioxide. For example, Japanese Patent JP 47-31981 discloses synthesis of alkylene carbonates from an epoxide and carbon dioxide in the presence of a Lewis acid (e.g ZnCl2, AlCl3 etc) and an organic base. The process was carried out at 100-400° C. and 19.6-294 bar CO2 pressure with 90% yield. Japanese Patent JP 51-13,720 discloses similar catalyst system where the temperature was 80-130° C. and pressure was less than 70.9 bar with approximately 90% yield. Chinese patent, CN1343668A by Deng et al teaches a process for synthesizing cyclic carbonate by a catalyst composed of azacyclic compound, non-metal halide and alkali metal halide or ammonium tetrabutyl bromide at temperature 100-140° C. and 1.5-4.5 MPa pressure.
U.S. Pat. No. 2003/0023109A1 by Schlosberg et al and WO 03/000641 A1 by Buchanan et al describe integrated process for preparation of dialkyl carabonates where the first step involves synthesis of cyclic carbonates using halogen free alkyl ammonium salt catalysts at temperature 100-200° C. and CO2 pressure up to 1000 psig. U.S. Pat. No. 2,773,070 by Lichtenwalter et al discloses reaction of alkylene oxides with carbon dioxide in the presence of certain class of ammonium halides where the process was operated at 100-225° C. and pressure of more than 300 psig. U.S. Pat. No. 2,873,282 by McCellan at al used catalyst comprised of hydroxide, carbonate or bicarbonates of quaternary ammonium compounds and the process operates at 1000-1500 psig and at 150-175° C. U.S. Pat. No. 5,153,333 by Schubert et al discloses a process of preparing 2-oxo-1,3-dioxolanes comprises of reacting an epoxy compound with carbon dioxide at 60-200° C. at normal pressure in the presence of a quaternary phosphonium compound as catalyst. Japanese patent JP1975000077840 describes preparation of cyclic carbonates from epoxide and CO2 in good yield using a Grignard reagent and a N-containing compound. Russian patent RU2128658C1 by Dobyleva et al discloses a method of preparation of cyclic carbonates with a cobalt halide catalyst at temperature 130-150° C. and pressure of 1-1.5 MPa.
Though good conversion and selectivity have been achieved as reported in the literature, most of the reported catalytic systems carry at least one of the following disadvantages: (1) need for high concentration of catalyst, (2) instability of catalyst, (3) air-sensitivity, (4) need for co-solvent, (5) requirement of higher temperature/pressure, (6) difficulty in separating the catalyst after the reaction for reuse etc. So efficient catalyst composite operating at milder experimental conditions preferably without need for any organic solvents but with very high turn over number is of great interest.